In the construction industry, there is an increasing demand for high-precision positioning of machines such as graders and dozers. At a building site, both logistics and construction accuracy may call for individual tracking of each machine or vehicle at the site.
To this end, there are systems based on advanced tracking sensors and robotic total stations, which remotely track and measure a kinetic moving target and continuously send measured data to a controlling computer or the like.
Recently, three-dimensional (3D) machine control operations have become increasingly important. Three-dimensional data from design software is employed onboard a construction machine, facilitating a comprehensive site control. The kinetic movement of the construction machine is continuously monitored by means of surveying apparatus, and the position, orientation, attitude, etc. of the machine is forwarded to an on-board controlling computer. The on-board computer calculates control data for the construction machine, based on the current position and orientation as compared to the three-dimensional design.
If the construction machine is manually controlled by an operator, the operator is provided with an indication about the correctness of machine position. For example, the operator may be given information about height and angle for an earth-moving blade. Based on such information, the operator may alter the position of the blade accordingly, if required.
For an automated machine control system, a controlling computer controls the entire system and automatically changes the position of the construction machine according to the three-dimensional design by providing appropriate control signals for example to hydraulic valve control systems of the machine.
Various types of construction machines can be equipped with a machine control system of this kind. Graders and dozers have been the typical earth-moving machines which were controlled and monitored by such systems. More recently, pavers, rollers and excavators have also been controlled in this manner. However, machine control systems are not limited to just construction machines. Three-dimensional control systems may be used also in hydrographical marine applications and in real-time kinetic railroad measurements, to name a few.
In order to obtain the positional data about the construction machine, or an earth-moving blade attached to such machine, a target is typically mounted on the machine or on a blade or similar attached to the machine. The target may, for example, include retro-reflecting prisms which are used as targets for an electronic distance measurement beam emitted from a total station. Suitably, such prisms are circumferentially arranged in the target, in order to provide for the possibility of measuring target position from any direction. The target may alternatively, instead of using prisms, be provided with other reflecting surfaces, such as a reflecting tape. Various suitable types of targets for distance measurement are known in the art.
Moreover, in order to facilitate tracking of the target by means of a robotic total station, the target may comprise emitters, such as light emitting diodes or the like. Such emitters may be designed to emit a coded signal to the robotic total station in order to identify the target. For example, each construction machine or target at a site may be given a unique identity, and information about this identity may be emitted by means of these emitters. Any receiving total station may then compare this identity with a known set of identities, in order to determine which unique construction machine (or which target) it is currently tracking.
An active target having emitters according to the above also facilitates the robotic tracking, since a tracking function can be implemented in the total station separate from its distance measuring capabilities.
Hence, there are known systems for real-time tracking of machines and tools, as described above, at a work site. This is particularly convenient when using three-dimensional design, as explained.
However, although these systems have indeed been successful, there is still room for improvement. For example, when a robotic total station continuously tracks for example a blade on a vehicle, it can determine its kinetic movement but there is no way of knowing if the vehicle is moving in a forward direction or if it is reversing. In addition, if the vehicle is not moving at all, there is no way of determining the forward direction thereof. The prior art has required a plurality of targets mounted on a single machine or vehicle in order to allow determination of its rotational (or directional) position.